The present invention relates to data transmission systems and devices and, in particular, relates to data transmission over public switched telephone networks and various devices for carrying this out. The invention is directed to an improved overall combination for transmitting data between a transmitter and a receiver through a system which involves the use of public switched telephone networks. The invention also includes processes for carrying this out as well as particular devices for efficiently carrying out the process.
The transmission of information between sources continues to grow at a rapid rate and companies recognize the importance in having the capability to receive information and transmit information to other parties efficiently. This transmission of information is illustrated in facsimile transmission between parties where both printed and graphic information are transmitted easily. Other forms of data transmission include electronic mail, however, electronic mail normally requires the receiver to check his electronic "mailbox" and only once it is checked can he then receive the information.
Other examples of systems for transmitting of information include the telex system, however, this system requires dedicated transmission lines and particular skills for transmitting of the information. Although the telex system has been in place for many years, facsimile transmission is rapidly erroding the usage of telex and greatly decreasing the importance of telex. This rapid increase in facsimile transmission is possibly due to the simple manner in which the information is transmitted and the mode of transmission via the telephone and the public switched telephone network. Only very limited knowledge of a facsimile machine is required and the system is extremely user friendly.
The problems with facsimile transmission is that it operates best with a dedicated telephone line and the rate of transmission of the information is determined by the particular facsimile machine and the quality of the connection between the transmitter and the receiver. In cases of local calls, the telephone lines are normally sufficient to allow the transmitter to operate at full speed, however, in long distance calls, the quality of the line falls. The facsimile machines automatically adjust and reduce the speed of transmission to ensure the information is properly received. Thus, the facsimile machine operates possibly at its highest speed on a local call where there is no additional charge for time and at its slowest speed on long distance calls where the transmitter is paying for the connect time. The public switched telephone network is also a system designed for voice transmission and the facsimile machine is not using all the capability of that system in transmitting the data. The transmission of pure data is simpler and specialized systems have been designed for the transmission of this data at higher rates of speed while also providing error correction.
There remains a need to allow the effective transmission of data between a transmitter and a receiver combining the advantages of the public switched telephone network and the data transmission systems. These data transmission systems are typically referred to as "packet switched data networks".